The fatalities take the total number of British forces killed in the country since operations began in 2001 to 40.

One British soldier was killed and five others were described by the Ministry of Defence as "very seriously" injured with one less seriously wounded in a blast at 12.20pm local time in northern Helmand Province.

Nato said the troops' patrol had unwittingly strayed into an unmarked minefield.

Just over four hours earlier another British soldier died in action against insurgents.

Four others were injured, including one seriously.

Elsewhere two others were injured in a second engagement with insurgents in Helmand.

"One UK soldier was very seriously wounded and one other received serious injuries," the MoD said in a statement.

The third death followed an attack on Friday in which 27-year-old Fijian Ranger Anare Draiva of the 1st Battalion Royal Irish Regiment was killed.

Today another soldier from the same battalion died from injuries suffered in that attack.

Members of his family were with him when he died.

It is understood that the soldier, who has not been named, had been flown out of Afghanistan for treatment and his relatives had joined him.

The deaths came as the first Nimrod aircraft took off from RAF Kinloss in Moray, Scotland, since the crash at the weekend which claimed 14 lives.

The RAF had grounded all aircraft at Kinloss as a mark of respect after the crash near Kandahar on Saturday.

The first flight had been due to take off yesterday but was postponed after engineers discovered a "routine fault".

But at 7.51am today a Nimrod took off, carrying 13 crew from the station's 120 Squadron, on a morning training exercise.

Defence chiefs said earlier today that the bodies of the 14 victims of the crash would be flown back to RAF Kinloss, where 12 of those who died had been stationed, on Tuesday.

RAF Brize Norton in Oxfordshire is the UK's usual military arrival point.